Van Au

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Trends

Author Order

Document Type

Co-Authors

Stephen A. Madison

Unilever (India)

S. Padmaja

Madurai Kamaraj University

Suresh Das

Central Glass and Ceramic Research Institute

Prashant V. Kamat

University of Notre Dame

Cooperative Institutions

Indian Institute of Science Education and Research Thiruvananthapuram

National Institute for Interdisciplinary Science and Technology

Unilever (United States)

Central Glass and Ceramic Research Institute

Indian Institute of Science Education and Research Mohali

Nethradhama Superspeciality Eye Hospital

Indian Institute of Science Education and Research Berhampur

Indian Institute of Science Education and Research Kolkata

Indian Institute of Science Education and Research, Bhopal

Indian Institute of Science Education and Research, Tirupati

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

Formation of nitrous oxide from the reaction of peroxynitrite with sodium azide

Journal of the Chemical Society. Dalton transactions (1999)

S. Padmaja Van Au Stephen A. Madison

The reaction of peroxynitrite (oxoperoxonitrate) with azide ion (N3–), the residual starting material in the peroxynitrite preparation by the ozonolysis of azide, was investigated in phosphate and carbonate buffers. The observed rate constants (kobs) for the decay of peroxynitrite at pH 4.5 in the presence of azide up to 30 mM are within experimental error identical to the self decomposition rate of peroxynitrite indicating that the reaction is zero order in azide concentration. However, when the concentration of azide is increased beyond 40 mM a slight increase in kobs is noticed. From the dependence of kobs on the concentration of azide the second-order rate constants for the reaction of peroxynitrite with azide are determined to be 3.5 and 1.2 M–1 s–1 at pH 4.5 and 7.4 respectively. In the presence of added bicarbonate the reaction between peroxynitrite and azide is zero order in azide concentration. The reaction of peroxynitrite with azide led to the production of nitrous oxide (N2O) in the absence and presence of bicarbonate as identified by GC-MS analysis of the reaction mixture. At a given pH and peroxynitrite concentration, the yield of N2O increased linearly with an increase in the concentration of azide up to 100 mM and attained saturation beyond that. Under identical conditions, the yield of N2O obtained in the absence of bicarbonate is 50% more compared to that obtained in the presence of bicarbonate. Based on kinetics and product studies, it is proposed that the reaction of peroxynitrite with azide involves a one-electron oxidation of N3– to azide radical (N3˙) by the activated form of HOONO (HOONO*). Also that the combination between N3˙ and nitrogen dioxide (NO2˙) is rapid and leads to nitryl azide (N3NO2) as a transient intermediate and precursor for nitrous oxide (N2O). In the presence of bicarbonate the peroxynitrite–carbon dioxide adduct (ONOOCO2–) or the carbonate radical anion (CO3˙–) is proposed as a one-electron oxidant towards N3– forming N3˙. The proposed mechanism for N2O formation from nitryl azide is supported by high level ab initio calculations.

Sodium azide

Bicarbonate

10.1039/a901164a

Cite

Citations (7)

Free radical induced oxidation of the azo dye Acid Yellow 9

Journal of the Chemical Society. Perkin transactions II (1999)

Suresh Das Prashant V. Kamat S. Padmaja Van Au Stephen A. Madison

The kinetics and mechanism of the free radical oxidation of the azo dye, Acid Yellow 9, by sulfate radical anions and hydroxyl radicals have been studied using pulse radiolysis and product analysis. Sulfate radicals react via one electron oxidation, generating the dye radical cation, which has an absorption maximum centered on 470 nm. In basic solutions, the radical cation mainly undergoes deprotonation to yield the aminyl radical which has a strong absorption with a maximum centered on 370 nm, and the pKa for the radical cation is 5.5. Formation of a sulfated product, 1, is indicative of a coupling reaction between the radical cation and sulfate radical anions. Studies also indicate that the hydroxyl radicals react with the dye by both electron transfer as well as by adduct formation.

Radical ion

Hydroxyl radical

10.1039/a809720h

Cite

Citations (46)